- Reintroduction programs are increasingly being used to save animals from extinction and aid in their recovery. The California Condor (Gymnogyps californianus), one of the most endangered birds in the world, is a remarkable example of how reintroduction programs can help rapidly increase a species' population numbers and range following a population bottleneck. Despite these gains, condors remain a critically endangered species and are absent from the northern half of their historical range. Here I evaluated questions concerning the biological feasibility of reintroducing California Condors to their former range in the Pacific Northwest using a multidisciplinary approach, employing the fields of history, molecular ecology, and spatial modeling. A review of the historical evidence, including the archeological and paleontological record, use of condors in Native American culture, and early historical accounts of explorers and naturalists, suggest that condors were once widely distributed and likely abundant in the Pacific Northwest. It is also likely that they were breeding birds in the region, rather than seasonal migrants. Examination of 526 base pairs from the control region of mitochondrial DNA (mtDNA) harvested from California Condor museum samples (n = 67) and genetic founders of the captive population (n =14) revealed 18 haplotypes in the historical population, 14 of which have not been reported previously. Only three of these haplotypes survived the genetic bottleneck, indicating > 80% reduction in haplotype richness. This substantial loss of genetic diversity is consistent with the hypothesis that condor populations were relatively abundant at the time of Euro-American contact, but declined rapidly as a result of human causes. I found no spatial sorting of haplotypes in the historical population, which suggests historical gene flow between the Pacific Northwest and southern and central California. Therefore, conservation strategies should consider restoring rangewide metapopulation connectivity when planning future reintroductions. Finally, I developed and tested activity-specific ecological niche models (nesting, roosting, and feeding) to identify areas in the Pacific Northwest that have retained ecological characteristics similar to those where condors have been observed in the last several decades. These models were integrated with information on condor movement ecology and biology to produce predictive maps of reintroduction site suitability across California, Oregon, and Washington. Ecological niche models were consistent with published knowledge of California Condor ecology, had good predictive performance when tested with data withheld from model development, and identified several candidate reintroduction areas. Results suggest that > 70% of the modeled nesting habitat and > 60% of the modeled roosting and foraging habitat in Washington, Oregon, and California is currently unoccupied. Thus, there are large unoccupied regions of the California Condor’s historical range in the Pacific Northwest that still possess relevant ecological features similar to currently occupied habitats, and therefore warrant consideration for future reintroduction efforts. In summary, this study provides foundational information to inform condor reintroductions to the Pacific Northwest. Key findings include: (1) extensive evidence that condors previously occupied the Pacific Northwest, likely in large numbers, prior to Euro-American expansion; (2) the lack of historical population structure, suggestive of historical gene flow between condor populations in the Pacific Northwest and elsewhere in the range; and, (3) identification of several candidate reintroduction areas in the Pacific Northwest that have retained environmental conditions that appear suitable for condor recovery.